1. Field of the Invention
The present invention relates to a level shift circuit, and more particularly, to a level shift circuit of a source driver.
2. Description of the Prior Art
In LCD (Liquid Crystal Display) driving systems, a level shift circuit is frequently used to generate a high voltage output from a lower voltage input for a source driver to drive the liquid crystal cells of the LCD panel. Please refer to FIG. 1. FIG. 1 is a diagram illustrating a level shift circuit 100 according to the prior art. The level shift circuit 100 comprises a differential input pair cascaded with a cross-coupled pair coupled between a first supply voltage VDDA and a second supply voltage VSSA as shown in FIG. 1. Furthermore, the differential input pair comprises an NMOS transistor Ma having a control gate for receiving a first input signal Sa, and an NMOS transistor Mb having a control gate for receiving a second input signal Sb. The cross-coupled pair comprises a PMOS transistor Mc and a PMOS transistor Md for respectively outputting a first output signal Sout1 and a second output signal Sout2 according to the first input signal Sa and the second input signal Sb. Normally, the first input signal Sa and the second input signal Sb are configured as a differential signal within a voltage range, smaller than the voltage range of VDDA and VSSA. Therefore, when the first input signal Sa is at a logic high level and the second input signal Sb is at a logic low level, the PMOS transistor Mc and the PMOS transistor Md latch the first output signal Sout1 to the first supply voltage VDDA, and the NMOS transistor Ma discharges the second output signal Sout2 to the second supply voltage VSSA (and vice versa). Therefore, the level shift circuit 100 shifts the voltage level of the input signals Sa, Sb to the output voltage level of either the supply voltage VDDA or the ground voltage VSSA.